Oil shale is a sedimentary rock containing energy rich organic matter known as kerogen. Kerogen has a macromolecular structure, consisting of many large hydrocarbon chains with atoms of sulphur, nitrogen and oxygen. The processing of oil shale to recover the organic matter can be done by thermal retorting, pyrolysis and solvent extraction. Recent trends in processing of oil shale focus on more environmentally benign techniques.
This has led to the use of supercritical fluids as solvents for extraction of hydrocarbons from oil shale. Supercritical fluids exhibit properties that are intermediate between those of a gas and a liquid. The extraction using supercritical solvents is advantageous because of high densities, higher diffusion constants and lower viscosities than the corresponding liquids. These properties enable supercritical fluids to penetrate into matrices and to solubilize components which may be otherwise insoluble or only partially soluble in the solvents used. Several supercritical solvents such as methanol, toluene, carbon dioxide and water have been studied for extraction of kerogen from oil shale samples. Supercritical fluid extraction of bitumen from Utah oil sands has been studied with propane solvent by Subramanian et. al. However, there remains a need for solvents for the extraction of hydrocarbons from oil shale.
As disclosed herein, pentane at a temperature above the critical temperature of pentane, 197° C., and at a pressure above the critical pressure of pentane, 33.3 atmospheres, may be used for the extraction of hydrocarbons from oil shale.